Heart disease is the major cause of death in industrialized societies. Lifestyle changes and the many drugs available to reduce LDL cholesterol have done a great deal to reduce heart disease, and the major avenue to further therapeutic progress lies in learning how to raise HDL, a major protection against heart disease. The mouse is an excellent model for finding HDL genes because the quantitative trait loci (QTL) for HDL in mouse and human are found in concordant locations. During the last grant period, we searched for and identified many genes that underlie HDL QTL using newly developed bioinformatic resources and methods as well as the classic genetic approaches for narrowing QTL. We also obtained preliminary evidence that many of the QTL genes for HDL fall into two biological pathways: the reverse cholesterol transport pathway and the metabolic syndrome pathway. In this renewal, we propose to test the hypothesis that these two pathways are highly significant in HDL regulation and to identify many more of the genes involved. In connection with our bioinformatics work, we developed a new standard genetic map for the mouse by correcting the mismapped MIT markers and demonstrating that recalculating QTLs with the new map caused a significant percentage of QTLs to move by more than 10 cM. Therefore, the first aim of this proposal is to recalculate the QTL data for at least 24 HDL crosses and as many more as possible. During the last grant period, we also carried out a meta-analysis for HDL QTL combining all crosses from the literature. The results showed that 38 loci had combined LOD scores that reached significance;we have identified the QTL genes for about half of these loci. In this grant period our second aim will be to identify additional QTL genes starting with the most significant and working our way down the list. As we identify each additional QTL gene, we will determine how it fits into pathways of HDL metabolism. Of the QTL genes that we have tentatively identified, several have a known function in HDL metabolism but others are quite new, and the mechanisms by which they modulate HDL levels are completely unknown. Therefore in aim 3 we propose to obtain additional evidence by making genetically engineered models of these genes, either transgenes or knockouts/knockins. PUBLIC HEALTH RELEVANCE: The major goal is to identify the genes and pathways that affect HDL cholesterol, which provides protection against the leading cause of death, heart disease. Identifying these HDL genes will uncover novel drug targets, and understanding the pathways of HDL regulation will elucidate the drug targets likely to have the greatest impact on HDL. Raising HDL is predicted to decrease heart disease incidence.